The present invention relates to hot-melt construction adhesives for adhering thermoplastic porous films to a substrate.
Typically, disposable absorbent articles require an outer liquid impermeable polymeric film or backsheet to prevent absorbed liquid from passing through the article into contact with the wearers clothing or skin. As this liquid impermeable film layer is typically not breathable, not allowing passage of moisture vapor, the articles can become hot and uncomfortable and occasionally lead to skin rashes. In this regard, liquid impermeable microporous film has been proposed to make the absorbent article breathable. A common disposable microporous film is filled with particulate fillers in amounts greater than about 30 percent. However, these breathable particulate filled films are less desirable in terms of softness and feel and contamination to the tape.
U.S. Pat. No. 4,902,553 proposes a rattle free vapor permeable microporous polymeric film for use as a outer liquid impermeable backsheet for a disposable absorbent product such as a diaper or an incontinent product. This patent proposes using a liquid impermeable but vapor permeable microporous film, which would allow moisture vapor to escape reducing the tendency for the absorbent product to cause a rash, such as diaper rash or other types of skin irritation. The microporous film is a soft, rattle-free, vapor permeable, liquid impermeable film. The rattle free nature of the film is accomplished by inclusion of rattle reducing liquid additive materials in the film and by embossment. Other patents describing liquid additive containing microporous films include U.S. Pat. Nos. 4,539,256; 4,609,584; 4,726,989 or 4,824,719. The microporous films described in these patents are all well suited for use as a microporous liquid impermeable film in a hygienic or absorbent article. However, a problem with these films is that the films have a tendency to change from opaque to translucent at points of hot-melt adhesive contact. This is particularly noticeable and objectionable when the films are adhered to a substrate with conventional hot-melt adhesives in an intermittent adhesive pattern. This results in an aesthetically displeasing product that also has a weakened level of adhesion between the microporous film and the substrate. This is a particular problem when the liquid additive is a plasticizing oil, such as mineral oil. Although numerous formulations of conventional hot-melt pressure sensitive adhesives have been evaluated by the applicant to adhere these microporous films to conventional substrates all have uniformly resulted in clearing the film at the points of adhesive contact. This film clearing also tends to spread to adjacent areas of the film not in direct contact with the adhesive. After an extensive investigation and screening the Applicants have discovered adhesives which address the problems identified above particularly with respect to the above liquid additive containing microporous films.